1. Field of the Invention
The present invention relates to a wire-cut electric discharge machining system, and more particularly to a wire-cut electric discharge machining system in which a main cutting by a high-current, short-pulse discharge is combined with a second cutting by a low-current, pulse discharge.
2. Description of the Prior Art
A wire-cut electric discharge machine has various advantages, such as requiring no special operator skills to accurately cut a metal mold or the like having a complicated shape and, since the electrode for the electric discharge cutting is a wire, there is no need to manufacture a working electrode with some required configuration, as is needed in ordinary discharge machines. On account of these advantages, the wire-cut discharge machine has very wide application, but this machine has a drawback in that the cutting speed is low. In order to increase the cutting speed, the machine has undergone various improvements. In general, for raising the cutting speed, increasing the discharge frequency per unit time or the efficiency of one discharge can be considered, but the prior art employs a high-current, short-pulse discharge in many cases. Accordingly, it is unavoidable that the machined surface is degraded and becomes rough.
To improve the degraded surface roughness resulting from the main cutting, it is general practice in the art that the main cutting by the high-current, short-pulse discharge method is followed by a second cutting for cutting the machined surface by a low-current, pulse discharge at high speed. With this method, it is possible to obtain excellent surface roughness, comparable to the case of employing low-speed cutting by the low-current pulse discharge from the beginning. In the prior art, however, the second cutting takes place independently of the main cutting and, for example, in the case of die cutting, it is necessary to remove a scrap slug after the main cutting and re-set the cutting conditions for the second cutting, and in the case of punch cutting, it is necessary to perform the main cutting, leaving two or three portions of the machined area uncut, and carry out the second cutting after the main cutting. Accordingly, the main and the second cutting operations must be effected separately; this complicates operation and makes it impossible to automate the wire-cut electric discharge machine.